In a mobile communication system employing the “LTE (Long Term Evolution)” system specified in the 3GPP, a radio base station eNB1 which is a serving radio base station of mobile stations UE is configured to perform a handover of a mobile station UE to a neighbor radio base station eNB2, when “P1+offset1+hysteresis1<P2+offset2” becomes true for the mobile station.
Here, P1 is a reception power of a signal from the radio base station eNB1 in the mobile station UE, and P2 is a reception power of a signal from the neighbor radio base station eNB2 in the mobile station UE.
In addition, the offset1 and the hysteresis1 are own station parameters which are used in the radio base station eNB1. Each of the offsets and the hysteresis) may be a positive value or a negative value.
Moreover, the offset2 and the hysteresis2 are neighbor base station parameters which are used in the radio base station eNB2. Each of the offset2 and the hysteresis2 may be a positive value or a negative value.
Note that, the offset2 set in the radio base station eNB1 and the offset) set in the radio base station eNB2 are set in accordance with load conditions of an OAM (Operation And Maintenance) apparatus and a neighbor radio base station eNB.
Specifically, the radio base station eNB1 is configured to optimize the aforementioned offset1 and hysteresis1 in accordance with load information (Load Indication) received from the neighbor radio base station eNB2.
However, there is a problem in a conventional mobile communication system. Specifically, in the conventional mobile communication system, a neighbor radio base station parameter (“New offset2”) supposed to be used in the neighbor radio base station eNB2 is calculated in the radio base station eNB1, on the basis of the load condition of the neighbor radio base station eNB2, and then, the neighbor radio base station parameter is set and applied to a handover process of a mobile station UE within a serving area under the radio base station eNB1. However, when the neighbor radio base station eNB2 does not know the “new offset2”, which is set and applied to the radio base station eNB1, a “Ping Pong phenomenon” likely occurs, i.e., the mobile station UE is handed over to the radio base station eNB1 immediately, because an “old offset2” which is different from the “new offset2” is applied, after the mobile station UE is handed over to the neighbor radio base station eNB2.
For example, as shown in FIG. 8, when a mobile station UE exists at a point X, there is a problem that the radio base station eNB1 handovers the mobile station UE to the radio base station eNB2, because “P11+offset1+hysteresis1 (P13)<P21+new offset2 (P24)” is true, while the radio base station eNB2, handovers the mobile station UE to the radio base station eNB1 because “P21+old offset2+hysteresis2 (P23)<P11+offset1 (P12)” is true.
Moreover, when the mobile station UE exists at a point Y, there is a problem that the radio base station eNB2 handovers the mobile station UE to the radio base station eNB1 because “P21+old offset2+hysteresis2 (P23)<P11+offset1 (P12)” is true, while the radio base station eNB1 handovers the mobile station UE to the radio base station eNB2, because “P11+offset1+hysteresis1 (P13)<P21+new offset2 (P24)” is true.    NON-PATENT DOCUMENT 1: 3GPP TS36.423 V8.0.0